Day 11 / Mar 15 (Tue)¶

Goal¶

Developing Scala applications

Exercises¶

Converter¶

Create Converter class that converts Farenheits to Celcius.

Palindrome¶

Define palindrome method using pattern matching and recursion.

def palindrome(s: String): Boolean = ???

Review a solution in solutions/day011-palindrome.sc.

longest¶

// Exercise 4 page 103
// Create a function that takes a list of strings
// and returns the longest string in the list
// Hint: Use foldLeft

def longest(ss: List[String]): String = {
  // ss.maxBy(_.length)
  val maxStringCandidate = ""
  ss.foldLeft(maxStringCandidate) { (longestString, s) =>
    if (longestString.length < s.length) s else longestString
  }
}
// longest(List("abc","420","a8c33"))
// 1. (maxStringCandidate, "abc") => "abc"
// 2. ("abc", "420") => "abc"
// 3. ("abc", "a8c33") => "a8c33"

Size of The Longest Element¶

longest that returns the size of the longest element (not the element itself).

// longestSize(List("trzy")) == 4
def longestSize(ss: List[String]): Int = {
  val maxLenCandidate = 0
  ss.foldLeft(maxLenCandidate)((b, s) =>
    if (b < s.length) s.length else b
  )
}

Longest Strings¶

longest that returns the longest string(s) in the list (all that are of the longest size).

case class LongestAllPair(size: Int, ns: List[String])
def longestAll(ss: List[String]): List[String] = {
  val candidate = LongestAllPair(-1, List.empty[String])
  ss.foldLeft(candidate)((b, s) =>
    // s.length > "b" save s (and remove the acc)
    // s.length == "b" add s to whatever you collected so far
    // if s.length < "b" then drop s
    if (b.size == -1) {
      LongestAllPair(s.length, List(s))
    } else if (b.size < s.length) {
      LongestAllPair(s.length, List(s))
    } else if (b.size == s.length) {
      LongestAllPair(b.size, s +: b.ns)
    } else {
      b
    }
  ).ns
}

longestAll(List("", "", "")) == List("", "", "")
longestAll(List("one", "two", "no")) == List("one", "two")

Handling Command Line¶

Write a command-line application that prints out the minimum and maximum numbers out of numbers from command line.

object Main extends App {

  if (args.isEmpty) {
    println("ERROR: No arguments. Exiting...")
    sys.exit(0)
  }

  println(s"Number of arguments on command line: ${args.length}")

  // Ints assumed
  val ns = args.map(_.toInt).sorted
  println(s"Given the following arguments: ${ns.mkString(", ")}")

  println(s"Maximum value: ${ns.max}")
  println(s"Minimum value: ${ns.min}")
}

Scala Topics¶

Case Class¶

class Person(val name: String) {
  override def toString = {
    name
  }
}
object Person {
  def apply(name: String): Person = new Person(name)
}

val jacek = new Person("Jacek")
jacek.name // "Jacek"

jacek.toString

case class MyPerson(name: String)

Schedule¶

8:30 - 10:10
10:25 - 12:00